1. Field of the Invention
The present invention relates to an image data processor, and more particularly to an image data processor which enables the existence of variation in an image to be recognized by extracting a feature from image data and by comparing the extracted feature with the feature which has been extracted and stored in advance by a similar processing.
2. Description of the Prior Art
In case a monitor for monitoring a scene in a TV camera to automatically judge whether or not any change takes place in the image of the TV camera and which region the change takes place in is taken into consideration, the most promising system is that, in which the image is received and stored in advance so that the stored image is compared with the image being received at the monitoring time thereby to detect the difference inbetween.
Since, however, the quantity of the data of the whole region of the image is remarkably extensive, the capacity of the memory is so increased that the monitor as a whole becomes highly expensive if the data are directly stored and compared. On the other hand, since the values of the image data themselves are liable to be fluctuated in accordance with the intensity or incident angle of light, it is rather advantageous in view of the countermeasures for noises that any geometrical feature is extracted for comparison from the image data than that the comparison is made with the image data themselves. Upon production of the aforementioned monitor, therefore, it is the most important technique that the image data are tried to be compressed to a feature vector having as little data as possible.
From the standpoint thus far described, there has been conventionally proposed by the Inventors a system, in which an image picked up is divided into plural block regions and the image data divided in the respective block regions are coded for the respective regions so that the data thus coded are sequentially compared with the coded reference image data stored in advance for the respective regions and corresponding to the background in the respective block regions thereby to detect the degree of the change in the image by counting the block regions where the compared results become inconsistent (Reference should be made to U.S. Pat. No. 3,936,800.). According to the aforementioned system, each of the block regions divided is composed of a plurality of picture elements which are two-dimentionally, and the changing direction of the brightness for each of the aforementioned picture elements is judged to count the number of the picture elements in each direction so that the image of each region is coded into a feature vector. For example, a two-dimentional plane is divided in eight-directions, for which are provided counters, respectively, each of which is preset to generate an output "1" when a counting operation higher than a preset value is performed. Then, in accordance with the judged results of the changing direction of brightness for each picture element, a corresponding counter is brought into its counting operation so that the feature of one block region can be displayed with the codes of 8 bits composed of the outputs of eight counters when the judgements of the whole picture elements in the region are completed. The system thus far described has an advantage that the comparison of two image for each block region can be performed with data of eight bits irrespective of the number of the picture elements in said block region.
According to the system proposed in the aforementioned U.S. Pat. No. 3,936,800, more specifically, the classification in the direction of brightness for each picture element is performed by sequentially extracting a two dimentional partial region, which is composed of one group of picture elements of n.times.n, from an object image, by comparing the picture elements in n number of right and left sides to obtain a brightness gradient f.sub.x averaged in the X direction, and by similarly comparing the picture elements in n number of upper and lower sides to obtain a brightness gradient f.sub.y in the Y direction. From these two pieces of information, EQU .theta.=tan.sup.-1 (f.sub.y /f.sub.x)
is calculated, and to which direction the calculated value belongs is judged. The results thus obtained are generated as the brightness direction of the picture elements representative of the aforementioned block regions extracted. Thus, a classifying circuit requires various kinds of resistors for the calculations of the values .theta..